Assuming you do decide you want a car, you must be VERY careful.
Southern Europe is FULL of ripoff car hire companies - some multinational, some local. My advice is that even though the up front cost willl look more expensive, ONLY book with the international brands - that'll be Hertz, Avis, Europcar (Alamo/National/Enterprise are the same bunch in Europe) or Sixt. Book with one of these brands - do it through a broker if you want a better price but make sure you KNOW WHO THE FIRM IS before booking. Then decline ALL extra insurance and purchase excess insurance in the UK before your trip from somebody like insurance4carhire or similar.
This will give you the best chance of a decent car, a full to full fuel policy and no ridiculous 2 hour queues at airport rental car desks to be sold a load of extra rubbish you don't need and ripped off for prepaid fuel by somebody who pretends they can't speak English.
The savings are NOT worth it.